Field of Invention
The invention relates to optical fiber cables. More particularly, the invention relates to optical fiber cables having optical fiber ribbons therein.
Description of Related Art
Mass fusion splicing makes the use of optical fiber ribbons attractive in relatively very high fiber count cable structures, as this technology allows splicing of 12 ribbonized fibers in approximately the same time as is required to splice two or three individual fibers. Optical fiber ribbons are optical fibers bonded together as a ribbon of optical fibers. There are now market requirements for cables having 1000 to 5000 fibers, or more.
Optical fiber ribbons, including flat optical fiber ribbons, become problematic when cabled into relatively high fiber counts. Conventional flat optical fiber ribbons often are grouped into rectangular arrays, often referred to as stacks, when assembling the optical fiber cable. However, optical fiber cables usually need to be circular to be easily installed. Thus, the square peg, i.e., the rectangular ribbon stack, must fit in the round hole, i.e., the circular cable structure. Such conventional configurations lead to empty space in the cable structure.
Some existing optical fiber cable manufacturers have developed a partially bonded optical fiber ribbon, also referred to as a rollable ribbon, where the optical fibers forming the optical fiber ribbon are not bonded over their entire length. The optical fibers are bonded intermittently, thus allowing the optical fiber ribbon to be folded or rolled into an approximately cylindrical shape, allowing for better filling of the circular cable, resulting in more optical fibers to be included in a given cable diameter compared to optical fiber cables with conventional fully bonded ribbon structures.
Conventional cable structures that have been developed to use partially bonded optical fiber ribbons are patterned from traditional high-count copper twisted pair cables, with the addition of auxiliary strength members embedded in the cable sheath. In these conventional cable structures, the optical fiber ribbons are twisted together into bundles identified with helically twisted binder threads. These bundles are then twisted together again to form higher fiber count units. Such configurations create a relatively high density cable structure.
However, conventional partially bonded ribbon structures have issues associated with their cable fabrication and installation. For example, the nested nature of the bundle structure in the core of the cable makes mid-span access of a specific optical fiber unit problematic. Also, such cable structures add a layer of unfamiliarity to craft installers who are trained to handle loose-tube cable structures. Also, such cable structures make it relatively challenging to identify a specific optical fiber unit, e.g., for mid-span access. Also, in such cable structures, both the optical fiber ribbons within each bundle and the groups of bundles that make up the core of the cable structure must be twisted to be held together. For example, the ribbons within the bundles and the bundles themselves must be twisted with a continuous twist in either a clockwise or counterclockwise direction.
There also are manufacturing issues associated with conventional partially bonded ribbon structures. For example, the equipment used to twist the optical fiber ribbons into bundles is relatively large and costly, making it difficult to produce relatively high fiber count cables in lengths sufficient for large scale deployment. The required equipment also is not typically found in some modern optical cable producing facilities, making the cost of market entry prohibitive, and increasing cost for both suppliers and customers. Also, the binding of the optical fiber ribbon units requires relatively high speed binding equipment, which limits line speed and increases the mechanical complexity and cost of the production process.